Fragmentation is a common processing for the majority of meteoroids, and has been recorded by photography, videotaping, and radar remote sensing. To recognize the meteoroid fragmentation with radar remote sensing, high angular and range resolutions are helpful. In this study, multireceiver and multifrequency observation of meteor echoes using a high-power-large-aperture (HPLA) VHF atmospheric radar, operated at the central frequency of around 46.5 MHz, was carried out. The radar beam was steered to the geographic north and at 51^o zenith. Receiving was done using 20 receivers and 5 carrier frequencies (46.250, 46.375, 46.500, 46.625, 46.750 MHz) for executing angular and range imaging of the meteor echoes, respectively. Adaptive constrained methods such as Capon’s method and its modified version-norm-constrained Capon method were employed in the imaging process. As a result, the angular and range resolutions were improved greatly. Both meteor head echoes and long-duration range spread trail echoes (RSTEs, also known as non-specular meteor echoes) were observed simultaneously. It showed that range imaging was capable of resolving the evolution of RSTEs in the radar volume clearly, in which the branched RSTEs could be evidence of meteoroid fragmentation. On the other hand, angular imaging with single point of raw data (~0.015s) identified multiple echo centers of the meteor head echoes, which was also related to meteoroid fragmentation.

     Asteroids having perihelion distance q < 1.3 AU and aphelion distance Q > 0.983 AU are classified as near-Earth objects (NEOs), which are divided into different groups: Atira, Aten, Apollo, Amor. One of 23 known Atiras, 2020 AV2, the first Vatira (its orbits totally inside Venus' orbit) is discovered by the Twilight project of the Zwicky Transient Facility (ZTF) on January 4, 2020. Upon the discovery of the first Vatira-class asteroid, a couple of orbital studies of the short-term orbital evolution of 2020 AV2 have been performed and published (C. de la Fuente Marcos et al, 2020). In this present work, we performed an assessment of the long-term orbital evolution of known near-Earth objects and known Atiras under Yarkovsky effect by using the Mercury N-body code. In addition, we will evaluate the lifetime of NEOs. and present the assessment of the relationship of orbital dynamical evolution between Atira-class and Vatira-class asteroids.

Photopolarimeter measurements of airless bodies like the asteroids can be used to construct the phase-polarization curves characteristic of individual compositional classes. It means that fitting of the polarization data can be used to infer the physical properties of the surfaces like the albedos and the chemical compositions which provide additional information not readily achievable by other methods. The asteroidal polarimetric measurements require relatively high accuracy because the corresponding polarization values could be on the order of 0.5%. In this study, the Triple Range Imager and Polarimeter (TRIPOL) on the Lulin Observatory was carefully calibrated by observations of a number of unpolarized and polarized standard stars from which the instrumental precision can be characterized. Statistical analyses of the experimental data demonstrated that TRIPOL is suitable for asteroidal polarimetric observations. Some examples of the phase-polarization curves obtained for different types of asteroids are shown to support this conclusion.